An organic electroluminescence device is a spontaneous light emitting device which utilizes the principle that a fluorescent substance emits light by energy of recombination of holes injected from an anode and electrons injected from a cathode when an electric field is applied. Since an organic EL device of the laminate type driven under a low electric voltage was reported by C. W. Tang et al. of Eastman Kodak Company (C. W. Tang and S. A. Vanslyke, Applied Physics Letters, Volume 51, Pages 913, 1987), many studies have been conducted on organic EL devices using organic materials as the constituting materials. Tang et al. used a laminate structure using tris(8-hydroxyquinolinol aluminum) for the light emitting layer and a triphenyldiamine derivative for the hole transporting layer. Advantages of the laminate structure are that the efficiency of hole injection into the light emitting layer can be increased, that the efficiency of forming excited particles which are formed by blocking and recombining electrons injected from the cathode can be increased, and that excited particles formed among the light emitting layer can be enclosed. As the structure of the organic EL device, a two-layered structure having a hole transporting (injecting) layer and an electron transporting and light emitting layer and a three-layered structure having a hole transporting (injecting) layer, a light emitting layer and an electron transporting (injecting) layer are well known. To increase the efficiency of recombination of injected holes and electrons in the devices of the laminate type, the structure of the device and the process for forming the device have been studied.
As the light emitting material of the organic EL device, chelate complexes such as tris(8-quinolinolato)aluminum, coumarine derivatives, tetraphenylbutadiene derivatives, bisstyrylarylene derivatives and oxadiazole derivatives are known. It is reported that light in the visible region ranging from blue light to red light can be obtained by using these light emitting materials, and development of a device exhibiting color images is expected (refer to, for example, Patent literature 1, Patent literature 2, and Patent literature 3).
Further, a device using asymmetrical pyrene derivative as the light emitting material is disclosed in Patent literatures 4 to 7, and a device using an asymmetrical anthracene derivative as the light emitting material is disclosed in Patent literature 8. Although these derivatives are used as the material for emitting blue light, further improvements of the lifetime thereof have been desired. In addition, development of a derivative being not easily affected by oxidization has been desired because of low oxidative stability of existing derivatives.
Patent literature 1: Japanese Patent Application
Laid-Open No. Heisei 8 (1996)-239655
Patent literature 2: Japanese Patent Application
Laid-Open No. Heisei 7 (1995)-138561
Patent literature 3: Japanese Patent Application
Laid-Open No. Heisei 3 (1991)-200289
Patent literature 4: Japanese Patent Application
Laid-Open No. 2001-118682
Patent literature 5: Japanese Patent Application
Laid-Open No. 2002-63988
Patent literature 6: Japanese Patent Application
Laid-Open No. 2004-75567
Patent literature 7: Japanese Patent Application
Laid-Open No. 2004-83481
Patent literature 8: International PCT publication No. WO 04/018587